Breaking the Limit of Local Density of Optical States Modification via Plasmonic Charging

In 1946, Purcell proposed that integrating emitters into a resonant cavity can electromagnetically modify the local density of states (LDOS), thus affecting emitters' absorption and/or emission rates. This effect has been considered as the "standard answer" to explain emission modification, laying theoretical foundation for numerous applications. Here we report that for the interaction between semiconducting emitters and plasmonic resonators, Purcell effect cannot fully explain the modification of emitters' relaxation dynamics, in which plasmonic doping of hot electrons also plays a critical role. Specifically, by integrating quantum dots (QDs) into a grating-like plasmonic resonator, we can dope QDs with hot electrons that are produced during plasmon excitation. This makes excited carriers outnumber the absorbed photons, forming an asymmetric excitation in QDs. These carriers accumulate in the conduction band of the QDs, resulting a radiative emission at higher energy which cannot be enabled by LDOS modification and is hence beyond the explanation of Purcell effect. Our findings identify a new cavity-emitter interaction pathway, providing novel schemes for both fundamental studies, e.g. quantum electrodynamics, and practical applications, e.g. gain provision